Spatially Variable Electron Beams in Io's Northern Alfvén Wing and Downstream Region

Abstract

We report on 0.032–32 keV electron observations during two Juno flybys of Io on 30 December 2023 and 3 February 2024. The first explored Io's northern Alfvén wing, the second covering its downstream region, south of the plasma wake. Both had closest approach altitudes of ∼1,500 km. Lower fluxes of >32 eV electrons in the Io torus transitioned to higher fluxes of energized, field-aligned electrons within these regions. The electron fluxes were spatially variable within the Alfvén wing, highest at the boundaries, the distributions evolving from bi-directional to mono-directional as Juno traversed this region. Electron fluxes in the downstream region were also field-aligned, energized, and comparable to those during the northern flyby, supporting the interpretation of a glancing encounter with the southern Alfvén wing. The electron energy flux in these regions ranged from 1–15 and 2–22 mW m⁻², respectively, which are enhanced compared to estimates from Galileo.